Variable-flow rate oil pump

ABSTRACT

A variable-flow rate oil pump includes: a main oil pump; a subsidiary oil pump; a control valve provided with a spool valve body; a main discharge oil passage; a subsidiary discharge oil passage merging with the main discharge oil passage; a main relief oil passage branching from the main discharge oil passage; a subsidiary relief oil passage branching from the subsidiary discharge oil passage; and a check valve permitting a flow only in one direction from the upstream side to the downstream side of the subsidiary discharge oil passage. The control valve is positioned at respective intermediate points of the main relief oil passage and the subsidiary relief oil passage, and the control valve is positioned on the upstream side of the check valve in the subsidiary discharge oil passage, and an engine speed at which the subsidiary discharge oil passage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in particular to a variable-flow rate oil pump, which can send oil to an automobile engine at an appropriate pressure in accordance with a rotational speed thereof.

2. Description of the Related Art

Conventionally, there have been variable-flow rate oil pumps equipped with two pumps, namely, a main oil pump and a subsidiary oil pump, and an oil pressure adjustment valve which adjusts the respective discharge amounts thereof. Japanese Patent Application Publication No. 2013-204487 discloses one oil pump of this kind. Japanese Patent Application Publication No. 2013-204487 discloses an oil pump unit (101) provided with an oil path switching valve (121) which adjusts the supply oil pressure from a main oil pump (106) and a subsidiary oil pump (107) to an oil pressure supply destination.

SUMMARY OF THE INVENTION

The oil pump unit (101) disclosed in Japanese Patent Application Publication No. 2013-204487 is configured so as to smoothly adjust the flow direction of the oil discharged from the main oil pump (106) and the subsidiary oil pump (107) by an oil path switching valve (121), in such a manner that oil can be supplied to the engine at an even more appropriate pressure corresponding to the speed of the engine.

Looking at FIG. 7 of Japanese Patent Application Publication No. 2013-204487, it is interpreted that a non-reversing valve (145) is disposed downstream of the oil path switching valve (121). As described in paragraphs [0037] and [0043], it is only indicated that the non-reversing valve (145) permits a flow of oil from the oil path switching valve (121) to a merging section (142d), but shuts off the flow of oil from a main discharge flow passage (141) to the oil path switching valve (121). In this way, the relationship between the non-reversing valve (145) and the spool valve (123) is not disclosed in particular, and therefore the effect of the non-reversing valve (145) in improving fuel consumption is not disclosed or suggested. Therefore, the object of the present invention (the technical problem to be solved) is to provide a variable-flow rate oil pump in which fuel consumption can be improved further.

Therefore, as a result of thorough repeated research aimed at resolving the abovementioned problem, the present inventors resolved the abovementioned problem by configuring a first embodiment of the present invention as a variable-flow rate oil pump, including: a main oil pump; a subsidiary oil pump; a control valve provided with a spool valve body; a main discharge oil passage extending from the main oil pump; a subsidiary discharge oil passage extending from the subsidiary oil pump and merging with the main discharge oil passage; a main relief oil passage branching from the main discharge oil passage; a subsidiary relief oil passage branching from the subsidiary discharge oil passage; and a check valve permitting a flow only in one direction from an upstream side to a downstream side of the subsidiary discharge oil passage, wherein the control valve is positioned at respective intermediate points of the main relief oil passage and the subsidiary relief oil passage; the control valve is positioned on the upstream side of the check valve in the subsidiary discharge oil passage; and an engine speed at which the subsidiary discharge oil passage is shut off by the check valve is set to be lower than an engine speed at which the subsidiary discharge oil passage is shut off by the spool valve body.

The inventors resolved the abovementioned problem by configuring a second embodiment of the present invention as the variable-flow rate oil pump according to the first embodiment, wherein an engine speed at which oil is relieved from the subsidiary relief oil passage by movement of the spool valve body is set to be lower than the engine speed at which the subsidiary discharge oil passage is shut off by the check valve.

The inventors resolved the abovementioned problem by configuring a third embodiment of the present invention as a variable-flow rate oil pump, including: a main oil pump; a subsidiary oil pump; a control valve provided with a spool valve body; a main discharge oil passage extending from the main oil pump; a subsidiary discharge oil passage extending from the subsidiary oil pump and merging with the main discharge oil passage; a main relief oil passage branching from the main discharge oil passage; a subsidiary relief oil passage branching from the subsidiary discharge oil passage; and a check valve permitting a flow only in one direction from an upstream side to a downstream side of the subsidiary discharge oil passage, wherein the control valve is positioned at respective intermediate points of the main relief oil passage and the subsidiary relief oil passage; the control valve is positioned on the upstream side of the check valve in the subsidiary discharge oil passage; the subsidiary discharge oil passage is shut off by the check valve before the subsidiary discharge oil passage is shut off due to movement of the spool valve body to the rear side; and relief of oil in the subsidiary relief oil passage is performed before the subsidiary discharge oil passage is shut off by the check valve.

The inventors resolved the abovementioned problem by configuring a fourth embodiment of the present invention as the variable-flow rate oil pump according to the first or third embodiment, wherein a main relief inflow port, a main relief expulsion port, a subsidiary inflow port, a subsidiary outflow port, a subsidiary relief inflow port, and a subsidiary relief expulsion port are provided from the front side in a valve chamber of the control valve; the subsidiary inflow port is provided at the same position as the subsidiary outflow port in the axial direction; the subsidiary relief inflow port is provided at the same position as the subsidiary relief expulsion port in the axial direction; a small-diameter valve chamber is provided at the front end of the valve chamber; in the spool valve body, a pressure receiving valve section, a first large-diameter valve section, a second large-diameter valve section and a third large-diameter valve section are formed successively from the front side to the rear side in the axial direction; the first large-diameter valve section shuts off and enables communication between the main relief inflow port and the main relief expulsion port; the third large-diameter valve section is configured so as to shut off and enable communication between the subsidiary relief inflow port and the subsidiary relief expulsion port; the pressure receiving valve section is inserted into the small-diameter valve chamber, and an operation outflow/inflow port is formed at the front end of the small-diameter valve chamber; the operation outflow/inflow port communicates with an operating oil passage that branches from the main relief oil passage; an operating valve and an expulsion oil passage are provided at an intermediate point of the operating oil passage; and the operating valve is configured so as to switch between either one of communication between the operating oil passage and the main relief oil passage and communication between the operating oil passage and the expulsion oil passage.

The inventors resolved the abovementioned problem by configuring a fifth embodiment of the present invention as the variable-flow rate oil pump according to the fourth embodiment, wherein a length in the axial direction of the first large-diameter valve section of the spool valve body is smaller than a maximum interval in the axial direction between the main relief expulsion port and the subsidiary outflow port. The inventors resolved the abovementioned problem by configuring a sixth embodiment of the present invention as the variable-flow rate oil pump according to the fourth embodiment, wherein a length in the axial direction of the first large-diameter valve section of the spool valve body is equal to or greater than a maximum interval in the axial direction between the main relief expulsion port and the subsidiary outflow port.

In the present invention, the pressure of the oil discharged from the subsidiary pump increases as the engine speed increases from a low speed, and the spool valve body of the control valve moves towards the rear side from an initial state. Due to the movement of the spool valve body towards the rear side, the spool valve body performs a shut-off operation so as to gradually reduce the cross-sectional surface area of the subsidiary discharge oil passage and ultimately close same completely.

However, since the check valve which is positioned to the downstream side of the control valve in the subsidiary discharge oil passage shuts off the subsidiary discharge oil passage previously, the spool valve body does not completely close off the subsidiary discharge oil passage, hence the flow of oil in the subsidiary discharge oil passage is stopped. Consequently, the subsidiary oil pump stops sending oil to the engine, and the fuel consumption can be improved accordingly.

Therefore, it is possible to resolve the problem in the prior art, in which, when the spool valve body moves to the rear side and the cross-sectional surface area of the subsidiary discharge oil passage becomes smaller or narrower, then oil cannot be discharged readily from the subsidiary oil pump, and consequently, the oil pressure of the subsidiary oil pump rises, energy is lost and fuel consumption becomes worse.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic drawing of a partial cross-section showing the configuration of the variable-flow rate oil pump according to the present invention, FIG. 1B is an enlarged diagram showing a control valve and a partial cross-section of the vicinity thereof, FIG. 1C is a principal enlarged cross-sectional diagram showing a state where the axial-direction length of a first large-diameter valve section of a spool valve is smaller than a maximum interval between the main relief discharge port and the subsidiary discharge port, and FIG. 1D is a schematic drawing of a partial cross-section of an operating valve;

FIG. 2 is a schematic drawing showing an operation in a low speed range of the engine according to the present invention;

FIG. 3 is a schematic drawing showing an operation in an initial stage of a medium speed range of the engine according to the present invention;

FIG. 4 is a schematic drawing showing an operation in a middle stage of a medium speed range of the engine according to the present invention;

FIG. 5 is a schematic drawing showing an operation in a later stage of a medium speed range of the engine according to the present invention;

FIG. 6 is a schematic drawing showing an operation in an initial stage of a high speed range of the engine according to the present invention;

FIG. 7 is a schematic drawing showing an operation in a first-half middle stage of a high speed range of the engine according to the present invention;

FIG. 8 is a schematic drawing showing an operation in a second-half middle stage of a high speed range of the engine according to the present invention;

FIG. 9 is a schematic drawing showing an operation in a later stage of a high speed range of the engine according to the present invention;

FIG. 10 an enlarged cross sectional drawing showing a main part of a spool valve body, in which the length of a first large-diameter valve section of the spool valve body in the axial direction is set so to be greater than the maximum interval between a main relief expulsion port and a subsidiary outflow port; and

FIG. 11 is a graph showing the characteristics of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention is described below on the basis of the drawings. The variable-flow rate oil pump of the present invention is provided inside an oil circuit 3 which supplies oil to respective parts of an engine (see FIG. 1). The configuration of the present invention principally includes a main oil pump 1, a subsidiary oil pump 2, a control valve B, an operating valve 8, a check valve 7, a main discharge oil passage 31, a subsidiary discharge oil passage 41, a main relief oil passage 32 and a subsidiary relief oil passage 42. These are combined into one unit, which is a variable-flow rate oil pump A.

The main oil pump 1 and the subsidiary oil pump 2 can use pumps of a variety of types, but a trochoid type internal gear pump is particularly suitable. The main oil pump 1 and the subsidiary oil pump 2 have different theoretical discharge amounts, and the theoretical discharge amount of the main oil pump 1 is often set to be greater than that of the subsidiary oil pump 2, but in order to increase the amount of variation, the theoretical discharge amount of the subsidiary oil pump 2 may be made greater.

The main oil pump 1 is incorporated into the oil circuit 3, and supplies oil to an oil supply object 9, such as an engine incorporated into the oil circuit 3 (see FIG. 1A). The main discharge oil passage 31 extends from the discharge section of the main oil pump 1 and is connected to the oil supply object 9. The main discharge oil passage 31 is a portion of the oil circuit 3 (see FIG. 1A).

The subsidiary oil pump 2 is provided in parallel alignment with the main oil pump 1 in the oil circuit 3 (see FIG. 1A). The subsidiary oil pump 2 may be arranged adjacently to or in integrated fashion with the main oil pump of the oil circuit 3, a branch oil passage 36 may be provided from the oil circuit 3 for the purpose of the subsidiary oil pump 2, and the subsidiary oil pump 2 may be provided in the branch oil passage 36 (see FIG. 1A).

A main relief oil passage 32 branches from the main discharge oil passage 31, and when relieving of the main oil pump 1 is required, oil is relieved (expelled) via the main relief oil passage 32. A subsidiary discharge oil passage 41 which merges with the main discharge oil passage 31 is provided on the discharge side of the subsidiary oil pump 2.

A subsidiary relief oil passage 42 which branches from a position to the downstream side of the discharge side of the subsidiary oil pump 2 and which connects with the inlet side of the subsidiary oil pump 2 is provided in the subsidiary discharge oil passage 41. The subsidiary relief oil passage is used to relieve oil when the subsidiary oil pump 2 is required to relieve oil.

The oil passages of the subsidiary discharge oil passage 41, the main relief oil passage 32 and the subsidiary relief oil passage 42 are concentrated into one control valve B, and the control valve B is arranged at an appropriate position that is midway between the respective oil passages (see FIG. 1B). In other words, the control valve B controls the connection and disconnection of the flow of oil that is discharged from the main oil pump 1 and the subsidiary oil pump 2.

The control valve B is configured by a valve chamber 5 and a spool valve body 6, and the spool valve body 6 is accommodated in the valve chamber 5 (see FIG. 1B). In the spool valve body 6, a first large-diameter valve section 61, a second large-diameter valve section 62 and a third large-diameter valve section 63 are arranged in sequence from the front side, and these sections are coupled via a coupling shaft 65. Furthermore, a pressure receiving valve section 64 is formed to the front side of the first large-diameter valve section 61. The pressure receiving valve section 64 and the first large-diameter valve section 61 are coupled by the coupling shaft 65 (see FIG. 1B).

Here, in the present specification, when describing the front side and the rear side of the control valve B, the side of the pressure receiving valve section 64 or an operation outflow/inflow port 54 a (described below), with reference to the spool valve body 6, is regarded as the front side in the axial direction, and the third large-diameter valve section 63 side or an elastic member 66 (described below) side of the spool valve body 6 is regarded as the rear side in the axial direction.

With respect to the front side and the rear side of the valve chamber 5, the same direction as the front side of the spool valve body 6 which is accommodated in the valve chamber 5 is regarded as the front side of the valve chamber 5, and the opposite side thereof is regarded as the rear side; the front side and the rear side are depicted in FIG. 1B. The front side and the rear side of the control valve B can also be used when the control valve B is arranged vertically, as well as when the control valve B is arranged horizontally as depicted in the drawings. For example, when the control valve B is arranged vertically with the front side upwards, then the upper side is the front side and the lower side is the rear side.

In the spool valve body 6, the diameter of the coupling shaft 65 is smaller than the diameters of the pressure receiving valve section 64, the first large-diameter valve section 61, the second large-diameter valve section 62 and the third large-diameter valve section 63. Furthermore, the diameter of the pressure-receiving valve section 64 is smaller than the diameters of the first large-diameter valve section 61, the second large-diameter valve section 62 and the third large-diameter valve section 63. The first large-diameter valve section 61, the second large-diameter valve section 62 and the third large-diameter valve section 63 are substantially the same (see FIG. 1B).

Gap sections exist between the pressure receiving valve section 64, the first large-diameter valve section 61, the second large-diameter valve section 62 and the third large-diameter valve section 63; the gap between the pressure receiving valve section 64 and the first large-diameter valve section 61 is called a first gap section 61 s, the gap between the first large-diameter valve section 61 and the second large-diameter valve section 62 is called a second gap section 62 s, and the gap between the second large-diameter valve section 62 and the third large-diameter valve section 63 is called a third gap section 63 s (see FIG. 1B).

The spool valve body 6 can move reciprocally forwards and backwards in the axial direction inside the valve chamber 5, an elastic member 66, such as a compression coil spring, is provided between the rear end side of the spool valve body 6, in other words, the third large-diameter valve section 63, and the rear end side of the valve chamber 5, and the spool valve body 6 is elastically impelled to the front side of the valve chamber 5 at all times. A state where the spool valve body 6 is stationary at the furthest possible position on the front side of the valve chamber 5 is called the initial state.

A small-diameter valve chamber 54 into which the pressure receiving valve section 64 is inserted is formed in the front-side end section of the valve chamber 5. As described below, oil is fed to the small-diameter valve chamber 54 via an operating oil passage 34 which branches from the main relief oil passage 32, as described below, and the pressure receiving valve section 64 on the front side is pressed to the rear side and the spool valve body 6 moves to the rear side.

A subsidiary inflow port 51 a, a subsidiary outflow port 51 b, a subsidiary relief inflow port 52 a and a subsidiary relief expulsion port 52 b are formed in the valve chamber 5 as a connecting portion relating to the subsidiary oil pump 2. Furthermore, a main relief inflow port 53 a and a main relief expulsion port 53 b are provided in the valve chamber 5 as a connecting portion relating to the main oil pump 1.

The main relief inflow port 53 a, main relief expulsion port 53 b, subsidiary outflow port 51 b and subsidiary relief expulsion port 52 b are formed in sequence from the front side of the valve chamber 5, the subsidiary inflow port 51 a is situated at the same position as the subsidiary outflow port 51 b in the axial direction, and the subsidiary relief inflow port 52 a is situated at the same position as the subsidiary relief expulsion port 52 b in the axial direction (see FIG. 1B).

Communication between the main relief inflow port 53 a and the main relief expulsion port 53 b, and between the subsidiary inflow port 51 a and the subsidiary outflow port 51 b, is enabled and shut off by the first large-diameter valve section 61 and the second large-diameter valve section 62 of the spool valve body 6 (see FIG. 2 to FIG. 9). Furthermore, communication between the subsidiary relief inflow port 52 a and the subsidiary relief expulsion port 52 b is enabled and shut off by the third large-diameter valve section 63 and the second large-diameter valve section 62 (see FIG. 2 to FIG. 9).

The subsidiary discharge oil passage 41 is divided into a first subsidiary discharge oil passage 41 a which is connected to the subsidiary inflow port 51 a side with respect to the control valve B that is provided at a midway position, and a second subsidiary discharge oil passage 41 b which is connected to the subsidiary outflow port 51 b (see FIG. 1A). The first subsidiary discharge oil passage 41 a connects the subsidiary oil pump 2 and the control valve B, and the second subsidiary discharge oil passage 41 b connects the control valve B and the main discharge oil passage 31 (see FIG. 1A).

Furthermore, the subsidiary relief oil passage 42 is divided into a first subsidiary relief oil passage 42 a which is connected to the subsidiary relief inflow port 52 a side with reference to the control valve B that is provided at a midway position, and a second subsidiary relief oil passage 42 b which is connected to the subsidiary relief expulsion port 52 b. The first subsidiary relief oil passage 42 a branches from the first subsidiary discharge oil passage 41 a and is connected to the subsidiary relief inflow port 52 a. Furthermore, the second subsidiary relief oil passage 42 b is connected from the subsidiary relief expulsion port 52 b to the inlet side of the subsidiary oil pump 2 or the branch oil passage 36 for the subsidiary oil pump 2.

The main relief oil passage 32 is divided into a first main relief oil passage 32 a which is connected to the main relief inflow port 53 a, with respect to the control valve B, and a second main relief oil passage 32 b which is connected to the main relief expulsion port 53 b side (see FIG. 1A). The second main relief oil passage 32 b is connected to merge at the inlet side of the main oil pump 1 or at a position to the upstream side of the main oil pump 1 of the oil circuit 3.

An operation outflow/inflow port 54 a is formed in the small-diameter valve chamber 54 of the valve chamber 5. An operating oil passage 34 is connected between the operation outflow/inflow port 54 a and the first main relief oil passage 32 a. An operating valve 8 is disposed at a midway point of the operating oil passage 34.

The operating valve 8 is provided with a direction control valve section 81. Furthermore, an expulsion oil passage 35 is provided in the operating valve 8. By the operation of the operating valve 8, it is possible to switch to either one only of communication between the operation outflow/inflow port 54 a and the first main relief oil passage 32 a, and communication between the operation outflow/inflow port 54 a and the expulsion oil passage 35 (see FIGS. 1B, 1D). The operating valve 8 employs a solenoid valve, but may also use a hydraulic type of valve.

A check valve 7 is provided in the second subsidiary discharge oil passage 41 b of the subsidiary discharge oil passage 41. The check valve 7 is used as a non-reversing. valve (see FIG. 1B). The check valve 7 permits a flow of oil only from the upstream side to the downstream side of the second subsidiary discharge oil passage 41 b, and shuts off the flow of oil in the opposite direction.

In other words, oil can only be sent from the subsidiary outflow port 51 b of the control valve B in a direction that merges with the main discharge oil passage 31, but cannot be sent in the opposite direction. The check valve 7 is configured by a sphere body 71 and an elastic impelling member 72, such as a compression coil spring, which impels the sphere body 71 (see FIG. 1B).

Furthermore, due to the elastic impelling member 72, the sphere body 71 of the check valve 7 acts so as to shut off the flow from the upstream side to the downstream side of the second subsidiary discharge oil passage 41 b, and when the flow speed of the oil flowing out from the subsidiary outflow port 51 b of the control valve B is small, the force of the elastic impelling member 72 is greater than the force of the oil pressure differential caused by the flow speed, and therefore the flow of oil can be stopped.

Moreover, in the control valve B, the length La of the first large-diameter valve section 61 of the spool valve body 6 in the axial direction is set to be smaller than the maximum interval Lb in the axial direction between the main relief expulsion port 53 b and the subsidiary outflow port 51 b of the valve chamber 5.

In other words,

La<Lb.

The first large-diameter valve section 61 does not completely close off both the main relief expulsion port 53 b and the subsidiary outflow port 51 b of the valve chamber 5 simultaneously, but rather leaves one thereof open. In other words, before the first large-diameter valve section 61 finishes closing off the subsidiary outflow port 51 b, the main relief expulsion port 53 b opens and relief of the main oil pump 1 can be started. Consequently, it is possible to stop the discharge of oil into the subsidiary discharge oil passage 41 of the subsidiary oil pump 2, and to start relief of the main oil pump 1, in a smooth fashion, and sudden changes in pressure can be prevented, which means that vibrations and noise can be reduced.

Furthermore, in the control valve B, the length La of the first large-diameter valve section 61 of the spool valve body in the axial direction is set so to be the same as, or greater than, the maximum interval Lb in the axial direction between the main relief expulsion port 53 b and the subsidiary outflow port 51 b of the valve chamber 5 (see FIG. 10).

In other words,

La≧Lb.

With the abovementioned dimensional relationship, the engine speed at which the oil discharged from the main oil pump 1 is relieved from the main relief oil passage 32 can be moved slightly to the higher speed range. In other words, by extending the engine speed of the (later-stage) medium speed range, where the oil pressure is low, towards the high speed range, it is possible to improve fuel consumption.

Next, the operation of the present invention will be explained principally in respect of the low speed range, the medium speed range and the high speed range of the engine. In the drawings, the arrows depicted along the respective oil paths indicate the flow of the oil. The rotational states of the engine also include idling (also called “idle rotation”).

In the low speed range of the engine, as shown in FIG. 2, the state of the spool valve body 6 of the control valve B is in an initial state. The first large-diameter valve section closes the main relief expulsion port 53 b and the second gap section 62 s opens the subsidiary inflow port 51 a and the subsidiary outflow port 51 b. Furthermore, the third large-diameter valve section 63 closes the subsidiary relief inflow port 52 a and the subsidiary relief expulsion port 52 b.

Furthermore, the operating valve 8 is set to a state of communicating the main relief oil passage 32 and the operating oil passage 34, and oil flows into the small-diameter valve chamber 54 from the operation outflow/inflow port 54 a, but the force due to this oil pressure is smaller than the elastic force of the elastic member 66 and the spool valve body 6 is in the initial state.

Consequently, the main oil pump 1 discharges oil to the main discharge oil passage 31, and supplies oil to an oil supply object 9, such as an engine. The main oil pump 1 and the subsidiary oil pump 2 do not both relieve oil. The subsidiary oil pump 2 discharges oil to the subsidiary discharge oil passage 41, and supplies oil directly to the oil supply object 9 from the merging point with the main discharge oil passage 31.

In other words, the main oil pump 1 and the subsidiary oil pump 2 both supply the full discharge amount, without alteration, to the oil supply object 9. Here, the force generated by the flow speed of the oil from the subsidiary oil pump 2, which acts on the check valve 7 that is provided in the second subsidiary discharge oil passage 41 b, is greater than the elastic force of the elastic impelling member 72 and therefore the oil flows through the second subsidiary discharge oil passage 41 b.

Next, the medium speed range of the engine is described, separately in terms of an initial stage immediately after transition to the medium speed range, a middle stage where the engine speed is medium, and a later stage close to the high speed range, as shown in FIG. 3 to FIG. 5. Immediately after transition from the low speed range to the medium speed range, the pressure of the oil flowing into the small-diameter valve chamber 54 increases, the force due to this oil pressure becomes greater than the elastic force of the elastic member 66, and the spool valve body 6 moves slightly to the rear side. The third large-diameter valve section 63 moves and the subsidiary relief inflow port 52 a and the subsidiary relief expulsion port 52 b open. In other words, the third gap section 63 s is positioned at the subsidiary relief inflow port 52 a and the subsidiary relief expulsion port 52 b.

However, in the initial state of the medium speed range, the spool valve body 6 moves by only a small amount, and therefore the subsidiary relief inflow port 52 a and the subsidiary relief expulsion port 52 b move slightly from a shut state to an open state, and relief of a small amount is started (see FIG. 3). In other words, the subsidiary oil pump supplies oil to the main discharge oil passage 31 via the subsidiary discharge oil passage 41, as well as relieving a slight amount of oil.

In the middle stage of the medium speed range, the spool valve body 6 of the control valve B moves further to the rear side. Consequently, the first large-diameter valve section 61 closes the subsidiary inflow port 51 a and the subsidiary outflow port 51 b so as to assume a very small opening surface area. At this stage, the oil discharged from the subsidiary oil pump 2 flows from the subsidiary inflow port 51 a to the subsidiary outflow port 51 b, but the force generated by the flow speed of the oil in this case is smaller than the elastic force of the elastic impelling member 72 of the check valve 7. As a result of this, the check valve 7 stops the flow of oil.

Consequently, the supply of oil from the subsidiary oil pump 2 to the oil supply object 9 is halted, and the subsidiary oil pump 2 only performs a relief operation. Furthermore, oil is supplied to the oil supply object 9 from the main oil pump 1 only. In this case, a relief operation by the main oil pump 1 does not start.

In the later stage of the medium speed range, as shown in FIG. 5, the spool valve body 6 of the control valve B moves further to the rear side. The first large-diameter valve section 61 becomes situated to the rear side of the position of the main relief inflow port 53 a and the main relief expulsion port 53 b, and the first gap section 61 s is positioned between the main relief inflow port 53 a and the main relief expulsion port 53 b and communicates these with each other.

The first main relief oil passage 32 a and the second main relief oil passage 32 b are communicated, and relief by the main oil pump 1 is started via the main relief oil passage 32. In other words, the main oil pump 1 carries out a relief operation, at the same time as supplying oil from the main discharge oil passage 31 to the oil supply object 9.

Next, the high speed range of the engine will be described separately in terms of an initial stage, a first-half middle stage, a second-half middle stage, and a later stage, as shown in FIG. 6 to FIG. 9. In the initial stage of the high speed range, as shown in FIG. 6, the operating valve is operated, and the operating oil passage 34 and the expulsion oil passage 35 are communicated with each other. Consequently, the oil inside the small-diameter valve chamber 54 of the valve chamber 5 is expelled from the expulsion oil passage 35, and the spool valve body 6 is moved to the front side by the elastic member 66. In other words, the spool valve body 6 is in the same initial state as the low speed range.

The first large-diameter valve section 61 opens the subsidiary inflow port 51 a and the subsidiary outflow port 51 b, and communicates the first subsidiary discharge oil passage 41 a and the second subsidiary discharge oil passage 41 b with each other, via the second gap section 62 s. Consequently, the oil flows again into the subsidiary discharge oil passage 41, and oil is supplied to the oil supply object 9 from the main discharge oil passage 31. In other words, the oil is supplied to the oil supply object 9 by the main oil pump 1 and the subsidiary oil pump 2.

In the first-half of the middle stage of the high speed range, as shown in FIG. 7, oil is sent into the main relief inflow port 53 a of the control valve B from the main discharge oil passage 31, due to the increase in the discharge pressure of the main oil pump 1. A force due to the oil pressure is then applied to the first large-diameter valve section 61, and the spool valve body 6 moves to the rear side. Furthermore, the configuration is such that, in the first-half of the middle stage of the high speed range, an oil pressure is not applied to the pressure receiving valve section 64 of the spool valve body 6, but since the pressure of the oil flowing in the first main relief oil passage 32 a is high, then the spool valve body 6 is moved only by the force of the oil pressure which is applied only to the pressure receiving surface of the first large-diameter valve section 61.

Due to this movement, the third large-diameter valve section 63 opens the subsidiary relief inflow port 52 a and the subsidiary relief expulsion port 52 b, and the first subsidiary discharge oil passage 41 a and the second subsidiary discharge oil passage 41 b are communicated with each other and relief by the subsidiary oil pump 2 is started. At this stage, the main oil pump 1 supplies oil to the oil supply object 9 without relieving oil, whereas the subsidiary oil pump 2 supplies oil to the oil supply object 9 while relieving oil.

In the second-half of the middle stage of the high speed range, as shown in FIG. 8, due to further increase in the discharge pressure of the main oil pump 1, the spool valve body 6 moves to the rear side. The subsidiary discharge oil passage 41 is shut off, and the subsidiary oil pump 2 performs oil relief only. The main oil pump 1 supplies oil to the oil supply object 9, but does not relieve oil.

In the later stage of the high speed range, as shown in FIG. 9, due to the further increase in the discharge pressure of the main oil pump 1, the spool valve body 6 moves to the rear side. The subsidiary discharge oil passage 41 is shut off and the subsidiary oil pump 2 performs oil relief only. The main oil pump 1 supplies oil to the oil supply object 9, as well as relieving oil. The relationship between the oil pressure and the engine speed in the low speed range, medium speed range and high speed range of the engine described above is depicted in the graph showing the characteristics of the present invention in FIG. 11.

In a second embodiment, by adopting a configuration in which oil is relieved from the subsidiary relief oil passage before the subsidiary discharge oil passage is shut off by the check valve, it is possible to further reduce the pressure of the subsidiary oil pump, and therefore further improvement in the fuel consumption can be achieved. In a third embodiment, it is possible to provide a variable-flow rate oil pump which can supply oil having an even more appropriate pressure in accordance with respective speed ranges of the oil supply object, such as an automobile engine. In particular, it is possible to set the pressure of the supplied oil precisely in respect of a medium speed range and high speed range of the engine, and hence the efficiency of lubrication can be further improved.

The check valve can prevent the flow of oil from the main discharge oil passage to the subsidiary discharge oil passage. In other words, reverse flow of oil in the subsidiary discharge oil passage is prevented and the work performed by the subsidiary oil pump can be performed accurately. Furthermore, the check valve is configured so as to shut off the oil passage when the oil pressure differential before and after the check valve generated by the flow speed of the subsidiary discharge oil passage is very small.

Consequently, the spool valve body moves to the rear side of the valve chamber, the subsidiary relief outflow port is not completely closed, and even if there is a slight gap in which the oil flows, the flow speed of the oil is weak and the check valve can stop the flow of oil in the subsidiary discharge oil passage. Furthermore, wasteful increase in the pressure of the oil supplied to the oil supply object from the subsidiary oil pump and via the main discharge oil passage can be suppressed. Apart from this, the same beneficial effects as those of claim 1 are obtained.

In a fourth embodiment, the configuration for moving the spool valve body can be simplified. The operating valve and expulsion oil passage are provided at an intermediate point of the operating oil passage, and the operating valve is configured so as to switch to either one of communication between the operating oil passage and the main relief oil passage, and communication between the operating oil passage and the expulsion oil passage, and therefore the movement operation of the spool valve body can be performed smoothly and reliably.

In a fifth embodiment, the length in the axial direction of the first large-diameter valve section of the spool valve body is smaller than the maximum interval in the axial direction between the main relief expulsion port and the subsidiary outflow port, and therefore it is possible to create a temporal overlap between the state immediately before stopping the supply of oil by the subsidiary discharge oil passage, and the state immediately after the start of a relief operation in the subsidiary relief oil passage, and shocks due to sudden changes in the oil pressure and/or the flow speed at the instant of changing operation can be diminished.

In a sixth embodiment, the length in the axial direction of the first large-diameter valve section of the spool valve body is configured to be equal to or greater than the maximum interval in the axial direction between the main relief expulsion port and the subsidiary outflow port, and therefore a relief operation by the main oil pump is started after the supply of oil via the subsidiary discharge oil passage is stopped, and hence reliable supply of oil and relief operation can be achieved. 

1. A variable-flow rate oil pump, comprising: a main oil pump; a subsidiary oil pump; a control valve provided with a spool valve body; a main discharge oil passage extending from the main oil pump; a subsidiary discharge oil passage extending from the subsidiary oil pump and merging with the main discharge oil passage; a main relief oil passage branching from the main discharge oil passage; a subsidiary relief oil passage branching from the subsidiary discharge oil passage; and a check valve permitting a flow only in one direction from an upstream side to a downstream side of the subsidiary discharge oil passage, wherein the control valve is positioned at respectively intermediate points of the main relief oil passage and the subsidiary relief oil passage; the control valve is positioned on the upstream side of the check valve in the subsidiary discharge oil passage; and an engine speed at which the subsidiary discharge oil passage is shut off by the check valve is set to be lower than an engine speed at which the subsidiary discharge oil passage is shut off by the spool valve body.
 2. The variable-flow rate oil pump according to claim 1, wherein an engine speed at which oil is relieved from the subsidiary relief oil passage by movement of the spool valve body is set to be lower than the engine speed at which the subsidiary discharge oil passage is shut off by the check valve.
 3. A variable-flow rate oil pump, comprising: a main oil pump; a subsidiary oil pump; a control valve provided with a spool valve body; a main discharge oil passage extending from the main oil pump; a subsidiary discharge oil passage extending from the subsidiary oil pump and merging with the main discharge oil passage; a main relief oil passage branching from the main discharge oil passage; a subsidiary relief oil passage branching from the subsidiary discharge oil passage; and a check valve permitting a flow only in one direction from an upstream side to a downstream side of the subsidiary discharge oil passage, wherein the control valve is positioned at respective intermediate points of the main relief oil passage and the subsidiary relief oil passage; the control valve is positioned on the upstream side of the check valve in the subsidiary discharge oil passage; the subsidiary discharge oil passage is shut off by the check valve before the subsidiary discharge oil passage is shut off due to movement of the spool valve body to the rear side; and relief of oil in the subsidiary relief oil passage is performed before the subsidiary discharge oil passage is shut off by the check valve.
 4. The variable-flow rate oil pump according to claim 1, wherein a main relief inflow port, a main relief expulsion port, a subsidiary inflow port, a subsidiary outflow port, a subsidiary relief inflow port, and a subsidiary relief expulsion port are provided from the front side in a valve chamber of the control valve; the subsidiary inflow port is provided at the same position as the subsidiary outflow port in the axial direction; the subsidiary relief inflow port is provided at the same position as the subsidiary relief expulsion port in the axial direction; a small-diameter valve chamber is provided at the front end of the valve chamber; in the spool valve body, a pressure receiving valve section, a first large-diameter valve section, a second large-diameter valve section and a third large-diameter valve section are formed successively from the front side to the rear side in the axial direction; the first large-diameter valve section shuts off and enables communication between the main relief inflow port and the main relief expulsion port; the third large-diameter valve section is configured so as to shut off and enable communication between the subsidiary relief inflow port and the subsidiary relief expulsion port; the pressure receiving valve section is inserted into the small-diameter valve chamber, and an operation outflow/inflow port is formed at the front end of the small-diameter valve chamber; the operation outflow/inflow port communicates with an operating oil passage that branches from the main relief oil passage; an operating valve and an expulsion oil passage are provided at an intermediate point of the operating oil passage; and the operating valve is configured so as to switch between either one of communication between the operating oil passage and the main relief oil passage and communication between the operating oil passage and the expulsion oil passage.
 5. The variable-flow rate oil pump according to claim 4, wherein a length in the axial direction of the first large-diameter valve section of the spool valve body is smaller than a maximum interval in the axial direction between the main relief expulsion port and the subsidiary outflow port.
 6. The variable-flow rate oil pump according to claim 4, wherein a length in the axial direction of the first large-diameter valve section of the spool valve body is equal to or greater than a maximum interval in the axial direction between the main relief expulsion port and the subsidiary outflow port.
 7. The variable-flow rate oil pump according to claim 3, wherein a main relief inflow port, a main relief expulsion port, a subsidiary inflow port, a subsidiary outflow port, a subsidiary relief inflow port, and a subsidiary relief expulsion port are provided from the front side in a valve chamber of the control valve; the subsidiary inflow port is provided at the same position as the subsidiary outflow port in the axial direction; the subsidiary relief inflow port is provided at the same position as the subsidiary relief expulsion port in the axial direction; a small-diameter valve chamber is provided at the front end of the valve chamber; in the spool valve body, a pressure receiving valve section, a first large-diameter valve section, a second large-diameter valve section and a third large-diameter valve section are formed successively from the front side to the rear side in the axial direction; the first large-diameter valve section shuts off and enables communication between the main relief inflow port and the main relief expulsion port; the third large-diameter valve section is configured so as to shut off and enable communication between the subsidiary relief inflow port and the subsidiary relief expulsion port; the pressure receiving valve section is inserted into the small-diameter valve chamber, and an operation outflow/inflow port is formed at the front end of the small-diameter valve chamber; the operation outflow/inflow port communicates with an operating oil passage that branches from the main relief oil passage; an operating valve and an expulsion oil passage are provided at an intermediate point of the operating oil passage; and the operating valve is configured so as to switch between either one of communication between the operating oil passage and the main relief oil passage and communication between the operating oil passage and the expulsion oil passage.
 8. The variable-flow rate oil pump according to claim 7, wherein a length in the axial direction of the first large-diameter valve section of the spool valve body is smaller than a maximum interval in the axial direction between the main relief expulsion port and the subsidiary outflow port.
 9. The variable-flow rate oil pump according to claim 7, wherein a length in the axial direction of the first large-diameter valve section of the spool valve body is equal to or greater than a maximum interval in the axial direction between the main relief expulsion port and the subsidiary outflow port. 